Of the myriads of developmental processes that define plant form and function, flowering is of exceptional interest to horticulturalists. The vast majority of horticulturally important crops are in some way dependent upon flowering, whether the flower is the primary goal of production, or is simply required for a crop to be produced. Much effort is currently expended into regulating the timing of flowering. In floriculture crops, the interest is in abbreviating or extending the vegetative phase in order to create an aesthetically pleasing balance between leaves and flowers, or to conveniently induce or repress flowering to take advantage of market potential. In ornamental foliage plants, and agronomically important plants that are grown for their leaf tissue (such as lettuce, spinach, and other greens), it is highly desirable to suppress flowering as long as possible. In other agronomically important plants grown for their seed products (such as fruits and vegetables as diverse as beans, peas, corn, and tomatoes), decreasing or increasing the time to flowering might expand the range where these crops could be grown, and might allow more precise control of nutrient flow to the crop. Also, in woody plants, there is a great deal of interest in finding means to abbreviate the vegetative phase, which in most species can last ten or more years and is probably the single most limiting factor for germplasm improvement through traditional breeding techniques.
Most efforts at controlling flowering time have involved manipulation of environmental conditions or the application of synthetic growth regulators. However, these approaches can increase production costs and labor requirements. In addition, the use of many traditionally utilized chemical compounds is becoming restricted. Alternative approaches to manipulate flowering, including the use of biotechnology, will require a better understanding of the associated molecular mechanisms.
The physiology and phenomenology of the developmental transition from vegetative growth to reproductive growth, or flowering, has been studied for many years, but only in the last decade have the molecular mechanisms come under examination. Flowering is ultimately determined by genes that govern the identity of the meristem, promoting or repressing a floral fate as opposed to a shoot or vegetative fate. There is incredible diversity of flowering strategies employed in nature, and it is becoming apparent that flowering at the molecular level involves an extraordinarily complex web of interactive pathways.
Although many genes have been identified that are involved in the regulation of flowering, it is clear that many more remain to be identified. Moreover, few of the identified genes have been cloned, and even fewer have been characterized as to their role in regulating flowering. Therefore, it would be useful to identify genes involved in flowering, to clone such genes, and to characterize the role of the genes in flowering. These genes would be useful in further understanding the regulation of flowering, as well as in the control of flowering in horticulturally important plants.